Primary for linear drive motor with solid steel stacks

ABSTRACT

A primary for a linear drive motor has a stage with stacks made from solid steel. Each stack has inner and outer teeth made that form a generally u-shaped cross-section for the stack. A magnet is disposed between the first and second stacks and a a coil wrapped between the first and second stacks. The stacks may be placed in a housing or may be formed as a housingless stage. The stacks and/or housing may be modified to selectively skew motor alignment to reduce motor cogging. The stacks may be contoured to follow various secondary forms. The stack inner and outer teeth lengths may be adjusted to help balance or optimize the magnetic circuit, to increase tooth surface area for increasing force, to allow more motor windings in the coil of the stack assembly, and to help locate the magnet and coil near the tooth surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of applicationSer. Nos. 13/179,959 and 13/180,017, both of which were filed on Jul.11, 2011, and are currently co-pending, the disclosures of which areboth incorporated by reference herein.

BACKGROUND

This disclosure relates to linear drive motors, including synchronouslinear drive motors. The disclosure relates to primaries and secondariesfor such motors, including stationary and moving primaries, stationaryand moving secondaries, and further including secondaries with andwithout magnets. In one aspect, as will be described in more detailbelow, a thin sheet of magnetic permeable material is formed with slotsextending through the material to form teeth of the secondary and thesheet may also have pockets or recesses formed simultaneously with themotor teeth to eliminate manufacturing or alignment variances. Some ofthe pockets or recesses may form teeth to be used as part of an encoderscale for the motor and other of the pockets or recesses may be used aspart of one or more sensors to provide positioning information for themotor, as well as sensors for the drive components regulatingcommutation of the motor, i.e., commutation teeth. In another aspect,the pockets used to provide the encoder and commutation functions may bealigned with small magnets installed in the secondary which are seen bythe encoder as “home” positions or limits. Yet in another aspect,pockets or recesses are added in the sheet and synchronized with thecommutation and encoder teeth to provide “absolute position” on a givenplaten secondary, thereby enabling the drive for the motor to beflexibly programmed, and the identifying of specific platen secondarieswhen many are strung together in a line and the providing of “absoluteposition” for the entire string. Thus, the concepts described hereinprovide for simultaneous formation (and synchronization) of the motorteeth with the encoder teeth and/or commutation teeth as well as otherdrive system components. A sheet formed in such a way to form asecondary eliminates the need of conventional “Hall Effect” devices andinherently minimizes problems with establishing or maintaining motorcommutation, for instance, motor commutation in sinusoidally commutatedlinear motors with platens having separate encoder scales that wereattached after the teeth in the platen were created. A sheet formed inthe way described herein reduces variation, thereby enabling the“electrical angle or commutation angle offset” of a motor to bestandardized which in turn reduces set-up and calibration times whileproviding increased flexibility. Moreover, a drive may electricallycouple a primary to a secondary in a string of secondaries and continueswith the same commutation pattern between the motor and encoder teethused in the previous secondary without needing to re-establish phasingin the next secondary. Motion is not slowed down or stopped to perform a“phase search” or read a “Hall Effect” sensor. The primary may also beformed from a solid steel stack and with reduced bearing requirements towork with the secondary to provide advantages in end user applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of one embodiment of a sheet for a platen segmentcomprising motor teeth etched through the sheet and encoder teethcomprising partially etched pockets or teeth synchronized with the motorteeth;

FIG. 2 is a cross sectional view of the sheet taken along lines 2-2 ofFIG. 1;

FIG. 3 is a cross sectional view of the sheet taken along lines 3-3 ofFIG. 1;

FIG. 4 is a cross sectional view of the sheet taken along lines 4-4 ofFIG. 1;

FIG. 5 is an enlarged cross-section view taken from detail area 5-5 ofFIG. 2;

FIG. 6 is a plan view of another embodiment of a sheet for a platensegment comprising motor teeth etched through the sheet, encoder teethcomprising partially etched pockets synchronized with the motor teeth,commutation teeth comprising partially etched pockets synchronized withthe motor teeth, and magnet locators comprising partially etched pocketssynchronized with the motor teeth and used as homes, limits or referencemarks for drive functions;

FIG. 7 is a cross sectional view of the sheet taken along lines 7-7 ofFIG. 6;

FIG. 8 is a cross sectional view of the sheet taken along lines 8-8 ofFIG. 6;

FIG. 9 is a cross sectional view of the sheet taken along lines 9-9 ofFIG. 6;

FIG. 10 is an enlarged cross-section view taken from detail area 10-10of FIG. 6;

FIG. 11 is a plan view of another embodiment of a sheet for a platensegment comprising stacked laminations with slots etched through each ofthe laminations having epoxy thereover and forming motor teeth, andencoder teeth comprising partially etched pockets in the top laminationsynchronized with the motor teeth, where the motor teeth have a greaterpitch that than shown in the sheet of FIG. 1;

FIG. 12 is a cross sectional view of the sheet taken along lines 12-12of FIG. 11;

FIG. 13 is a cross sectional view of the sheet taken along lines 13-13of FIG. 11;

FIG. 14 is a cross sectional view of the sheet taken along lines 14-14of FIG. 11;

FIG. 15 is an enlarged cross-section view taken from detail area 15-15of FIG. 12;

FIG. 16 is a plan view of another embodiment of a sheet for a platensegment comprising stacked laminations with motor teeth etched througheach of the laminations, with encoder teeth comprising partially etchedpockets serving as reference marks or teeth in the top laminationsynchronized with the motor teeth, commutation teeth comprisingpartially etched pockets in the top lamination synchronized with themotor teeth, and magnet locators comprising partially etched pocketsused as homes, limits or reference marks for drive functions in the toplamination which are synchronized with the motor and commutation teeth;

FIG. 17 is a cross sectional view of the sheet taken along lines 17-17of FIG. 16;

FIG. 18 is a cross sectional view of the sheet taken along lines 18-18of FIG. 16;

FIG. 19 is a cross sectional view of the sheet taken along lines 19-19of FIG. 16;

FIG. 20 is an enlarged cross-section view taken from detail area 20-20of FIG. 16;

FIG. 21 is a plan view of another embodiment of a sheet for a platensegment comprising stacked laminations with motor teeth etched througheach of the laminations, with encoder teeth comprising partially etchedpockets in the top lamination synchronized with the motor teeth,commutation teeth comprising partially etched pockets in the toplamination synchronized with the motor teeth and including additionalreference markers in the commutation track, and magnet locatorscomprising partially etched pockets for locators for small magnets inthe top lamination synchronized with the motor and commutation teeth;

FIG. 22 is a cross sectional view of the sheet taken along lines 22-22of FIG. 21;

FIG. 23 is a cross sectional view of the sheet taken along lines 23-23of FIG. 21;

FIG. 24 is a cross sectional view of the sheet taken along lines 24-24of FIG. 21;

FIG. 25 is an enlarged cross-section view taken from detail area 25-25of FIG. 22;

FIG. 26 is a plan view of an alternate embodiment of a sheet of a platensegment comprising a motor teeth etched through the sheet, with encoderteeth comprising partially etched pockets in the sheet synchronized withthe motor teeth, commutation teeth comprising partially etched pocketsin the sheet synchronized with the motor teeth, a track with additionalreference markers comprising partially etched pockets in the sheetsynchronized with the motor teeth, and partially etched pocketscomprising magnet locators in the sheet synchronized with the motorteeth;

FIG. 27 is an enlarged plan view of an alternate embodiment of a platencomprising slots etched through the sheet to hold motor magnets of asecondary, with encoder teeth comprising partially etched pockets in thesheet synchronized with the secondary magnet slots, commutation teethcomprising partially etched pockets in the sheet synchronized with themotor teeth with additional reference markers, and partially etchedpockets comprising magnet locators in the sheet synchronized with themotor teeth;

FIG. 28 is an exploded perspective view of a single axis linear drivemotor with a housing enclosure not shown but showing a primarycomprising three motor stacks, a secondary comprising a sheet formed inthe manner shown by any of the sets of figures above, a secondarysupport base for the sheet with integrated bearing rails, an encoder, aside magnetic preload; and a top and side bearing system for primary anda bearing system for the primary;

FIG. 29 shows the single axis linear drive motor of FIG. 28 withcomponents assembled into a housing from a perspective view oppositethat of FIG. 28;

FIG. 30 shows a motor stack that may be used with a secondary comprisinga sheet formed in the manner shown by any of the sets of figures above;and a bearing system therefor;

FIG. 31 shows the housingless motor of FIG. 30 with epoxy coating;

FIG. 32 is an alternate embodiment of a rotary motor with a single sheetspot welded to form a rotary motor primary;

FIG. 33 is an alternate embodiment of two sheets formed in a tubularshape and concentrically disposed about each other to form a rotarymotor primary;

FIG. 34 is an alternate embodiment of a rotary or limited or unlimitedtorque motor with an integrated vertical “z”-axis motor with motorstacks arranged orthogonally to create multi-axis capability;

FIG. 35 is an exploded perspective view of an exemplary platen segmentand curved support structure;

FIG. 36 is a perspective view of the platen segment and curved supportstructure of FIG. 35 assembled with an arcuate motor operatively coupledthereto for translation along the secondary;

FIG. 37 is an exploded side view of one embodiment of a primary stagecomprising a solid steel stack with an embedded roller bearing;

FIG. 38 is a top plan view of the primary stage of FIG. 37;

FIG. 39 is a bottom view of the primary stage of FIG. 37 with theembedded bearing assembly removed to show details of the recess formedin the stacks and magnet;

FIG. 40 is a bottom view of the primary stage of FIG. 37 with theembedded bearing assembly installed;

FIG. 41 is side cross-sectional view of the primary stage taken alonglines 41-41 of FIG. 37;

FIG. 42 is a side cross-sectional view of the primary stage taken alonglines 42-42 of FIG. 37;

FIG. 43 is an exploded perspective view of an alternate embodiment of aprimary stage showing the bottom face of the primary stage and gasbearing discharge ports for the primary stage;

FIG. 44 is an alternate embodiment of the primary stage of FIG. 30;

FIG. 45 is a bottom perspective view of a housing for a primary shownwith bearings and stacks removed;

FIG. 46 is an exploded perspective view showing stacks and bearingsassociated with the housing of FIG. 45;

FIG. 47 is a perspective view showing the stacks and bearing componentsinstalled in the housing of FIG. 45;

FIG. 48 is a bottom perspective view of a primary stage with installedstacks and bearings and applied and epoxy;

FIG. 49 is an alternate embodiment of a housing with an alternativebearing system and stack locator system to that shown in FIG. 45-47;

FIG. 50 is another embodiment of a primary stage with an alternativebearing system to that shown in FIG. 45-47 and FIG. 49;

FIG. 51 is an alternate embodiment of a solid steel stack shown in asemi-finished machined state;

FIG. 52 is a bottom perspective view of an alternate embodiment of ahousing with the stack of FIG. 51 mounted therein and finished machinedwith teeth and a slot;

FIG. 53 is a cross sectional view of assemblies of stacks of FIG. 51mounted on the housing of FIG. 52 and finished machined with teeth andslot, and coils installed in the stack assemblies;

FIG. 54 is an exploded bottom perspective view of a primaryincorporating the stacks of FIG. 51; and

FIG. 55 is a bottom perspective view of the primary of FIG. 54.

DETAILED DESCRIPTION

The description of the parent applications is in reference to asecondary for a linear drive motor. The secondary is shown in FIGS. 1-26and 28-29. The principles described in the parent applications may beused in connection with a rotary motor as shown in FIGS. 32-34, orpermanent magnet linear motor with magnets in the secondary like an ironcore motor or even a cog-free, for instance, as shown in FIG. 27.Additionally, the principles described in the parent applications relateto a linear drive motor where the primary moves and the secondary isstationary, and also a stationary primary and a moving secondary, forinstance, in a CNC conveyor system that moves and sorts items sitting onor fixtured to one or more platen segments, or positions items in aprecise way, for instance, in automated assembly, machining ormanufacture. The description herein is directed to the primary and abearing system that may be used in connection with the secondariesdescribed in the parent applications. The descriptions herein and in theparent applications should not be viewed in any limiting way. As withthe parent applications, for purposes of illustration, a linear drivemotor with a moving primary and a stationary secondary will bedescribed.

Motor Primary

The parent applications described and illustrated embodiments of lineardrive motor primaries with reference to FIGS. 28-31 and 35-36.Additional embodiments of the linear drive motors are described belowwith reference to FIGS. 37-55.

Referring to FIGS. 28-31 and 35-36, the linear drive motor 50 comprisesa moving primary carriage 52 with solid steel stacks 54 containing coils56 and magnets 58. The solid steel stacks are preferred in that they aremuch simpler in design and they may be machined from a single piece ofsteel rather than from laminations that are stamped, stacked and bondedtogether. Also, the solid steel stacks provide their own integralsupport without having to add intermediate supports. Other advantages ofthe solid steel stack are discussed in further detail below. The movingprimary carriage 52 may also comprise a machined housing 60 that holdsthe solid steel stacks, coils and magnets. The housing may also be anextruded piece. FIG. 28 shows the exploded view of the motor primarywithout a housing and FIG. 29 shows the linear motor with the housing 60enclosing the primary carriage components. The solid steel stacks 54with magnets may be mounted in a cavity and self-align with mountingholes in the moving primary carriage housing. The coils 56 may then beplaced into the stacks and the same housing 60 may be used as a mold forencapsulating the parts with epoxy. Because epoxy is not needed forstructural support in the stacks, a more suitable non-structural epoxyor another material may be selected, for example, one which has betterthermal conductivity, produces less “outgassing” and thus meetscleanroom requirements, or is better suited in a high vacuum operation.

As an alternative, a stack 62 as shown in FIG. 30 may be encapsulatedwith epoxy 64 as shown in FIG. 31 to form the primary without a housing(i.e., housingless). The epoxy fills the teeth and covers the stacks 62and coils 56 for electrical insulation, mechanical protection,aesthetic, or safety reasons. The customer may mount fixtures or toolingdirectly to the solid steel stack. External surfaces on the stacks maybe configured with mounting holes 68 for mounting components asnecessary based upon the end user application, including mounting acustomer's payload directly to the stack. The stacks may also beconfigured to support the encoder and bearings. As shown in FIG. 30, thestack has projections 70 and roller bearings 72 may be directly mountedto the stack projections. The stack has additional projections andcontours 73 to protect or hide end turns of the coils 56 under the motorteeth and reduce potential impingement from the bearings or alternatelyto provide greater tooth area which is oftentimes sacrificed in thedesign of some motors.

A linear encoder read head 74 (FIGS. 28,29) may be attached directly tothe motor carriage. The linear encoder read head 74 is part of thelinear encoder system that provides position feedback to the drive orcontroller of the motor. The linear encoder read head 74 reads anencoder scale provided on the secondary, as described below in greaterdetail, and eliminates the Hall Effect sensors that often are providedon the housing to establish motor commutation. The encoder read head maybe disposed in a mounting pocket adjacent a stack. By machining themounting pocket for the encoder read head along with mounting holes forthe stacks together, a fixed relationship between the motor stacks 54and encoder read head 74 may be accurately established and repeatedduring the manufacturing process. This fixes the “electrical orcommutation angle offset” for the primary thereby facilitating set upand interchanging component parts.

The primary carriage 52 may also have an arrangement of bearings 80 thatmay comprise relative simple and inexpensive roller bearing assemblies(about 3 or 4) which can handle the high magnetic preloads between theprimary and secondary. The roller bearings 80 may be configured forrolling contact with hardened wear surfaces of the support plate. Theroller bearings 80 may be mounted to the housing 60 using conventionalmeans and may replace expensive bearing blocks and precision machinedspacers often found in some linear drive motors. The roller bearings 80may be mounted into the housing shoulder screws with square nuts on theend of the screw which fit into slots on the housing to hold the bearingin place. Jack screws may be used to adjust the position of the shoulderscrew in the slot to achieve the desired motor air gap. The bearings maybe mounted to a solid steel stack in a similar way by machining a recessor pocket in the stack under the magnet to accommodate the square nutfor sliding motion therein, and a shoulder screw may be used to mountthe bearing. The bearing may also be mounted directly to the solid steelstack. Side guide bearings 82 may also be mounted to the housing (orstack) in a similar way. Holes 84 in the housing (or the stack) may beprovided for access to the jack screws. A magnetic preload assembly 86may be provided to hold the motor against the side of the platen. Themagnetic preload assembly 86 may be formed from a permanent magnetdisposed between two steel plates as shown in FIG. 28.

Additional embodiments of motor primaries are described below in greaterdetail and in reference to FIGS. 37-55.

Sheet Description

The linear drive motor stationary secondary 90 comprises a sheet 92 of ahighly magnetic permeable material, preferably with a high iron contentand low carbon content. The sheet may be fixed to a support structure 94to form a platen segment for the secondary. The support structure 94 maycomprise a relatively thicker plate with a pocket that receives thesheet, for instance, as shown in FIG. 28. The material forming thesupport structure 94 may be a high carbon steel or other hardened steelfor strength and wear resistance while the sheet 92 insert is made froma relatively soft yet highly magnetically permeable material. Thesupport structure 94 may have three precision ground and hardenedbearing surfaces 96 which are typically two on the top surface and oneguide surface on one side of the platen for the roller bearings 80 andside guide bearings 82 associated with the primary carriage. Thus, thesupport structure 94 may provide overall support for the platen segment,and bearing support for high magnetic preloads and customer loads, andguidance. A very thin hardened or tempered steel plate (not shown) maybe disposed between the support base and the sheet to provide a wearresistant surface for the roller bearings to contact. The wear strip maybe easily replaced when worn as necessary. Although the sheet is shownin the drawings as being insertable into a cavity 98 of a supportstructure to form a rigid and flat base for the secondary, the sheet maybe mounted to a flat surface. The sheet 92 may be secured, or mounted toa support structure 94, with screws, spot welds, or adhesive.

Additionally, a thin sheet 92 may be formed into a tube 102 as shown inFIGS. 32 and 34, or two sheets 92 a may be wrapped into concentricallydisposed tubes to form layers 102 a to form a rotor of a rotarypermanent magnet servo motor as shown in FIG. 33. Opposite side edges ofthe sheet may be attached together form the tubular shape. A thin sheet92 may also be mounted to the curved support 104 and conform to thecurved support as shown in FIGS. 35-36. Accordingly, the principlesdescribed herein may be used in connection with rotary servo motor andgear applications that require linear or rotary motion.

Referring to FIGS. 1-27, the sheet 92 preferably has a width 110 and alength 112, although both sides may be the same dimension, and a firstsurface 114 and an opposite second surface 116 with a thickness 118extending therebetween. The sheet thickness may be 0.060 inches to 0.100inches. A sheet may have a thickness of about 2 mm or (0.0787 inches).More highly magnetically permeable materials are readily available inthese thinner thicknesses. The sheet 92 has a plurality of slots 120 inthe first and second surfaces and at least partially extending throughthe sheet thickness parallel to the width 110 of the sheet and spacedalong the length 112 of the sheet. The slots define a plurality of teeth121 in the sheet between the slots and enable the sheet to beconformable to the mounting surface to which the sheet is mounted whenforming the secondary of the motor. The slots/teeth may have a spacingdefining a motor pitch.

Mounting holes 122 in the sheet may be added for mounting the sheet tothe base. Guide holes 124 may be provided in the sheet depending uponthe end user's application and requirement for external mounting offixtures and tooling. The guide holes 124 (and/or mounting holes 122)may be synchronized with the features of the sheet described herein(i.e., “Track 3” for absolute positioning disclosed below) to establisha common “zero position” among motor secondaries. Additionally, afterthe sheet is mounted to a support structure or base plate, the guideholes 124 may provide references for customer use, for instance,precision drilled holes for reaming and installation of dowel pins orfor tapped holes used in the end-user application.

Referring to FIGS. 1-26, the sheet may have a plurality of bridges 126formed in the slots between the teeth thereby operatively connecting theteeth 121 together. This ensures the spacing of motor teeth 121 isrelatively constant but yet allows the sheet to be handled in themanufacturing process without deforming the teeth and also to beconformable to the surface to which it is mounted. The bridges 126between the motor teeth 121 assist in keeping the teeth in a properspatial relationship when the sheet conforms to a curved supportstructure. The bridges 126 may form recesses in at least one of thefirst and second surfaces 114,116. Preferably, the bridges are about 25%of the sheet thickness, although the bridges may be the entire thicknessof the sheet. The bridges 126 may also be generally flush with either ofthe first and second surfaces as may be desired. Making the bridgesflush with the second surface reduces the effect of interference of theflux pattern between the primary and secondary caused by the bridges.Adjusting the thickness and the position of the bridge (i.e., flush orrecessed from either the first of second side) allows the relativepliability of the sheet to be changed as desired.

As shown in FIGS. 11-25, the sheet may include laminations 92 a stackedtogether to form the sheet. Each lamination may have a slot arrangementas described above so that when the laminations are stacked, they form acontiguous secondary. This allows the tooth height to be extended andthe tooth cross section to be selected for optimum conditions. Thus, thelaminations in the stack may be geometrically different and selectivelystacked to form a desired cross sectional geometry of the teeth of thesheet. As an example in FIGS. 12, 17, and 22, the sheet comprises twolaminations of about 2 mm (0.0787 inches) that are stacked to form a 4mm thick sheet for the platen. Accordingly, the tooth height has beendoubled which is desired when the motor pitch is doubled. This increasesforce with the larger tooth and produces greater velocities that may bedeveloped in the motor, especially in a large pitch motor. For largerpitch motors, laminations may be stacked as desired to provide a desiredtooth size. When stacking multiple laminations, the bridges may beformed narrower to reduce interference with the magnetic path betweenthe motor and secondary teeth. By way of illustration and not in anylimiting sense, the secondaries shown in FIGS. 11, 16, and 21 have a 10mm motor tooth pitch.

The slots in the sheet may be formed in such a way that the motor teethhave a cross section other than rectilinear. For instance, it has beenfound that a trapezoidal tooth has advantageous magnetic properties in alinear motor to produce more force. Accordingly, the width of the slot120 on the top side 114 of the sheet may be greater than the slot widthat the bottom side 116 of the sheet. FIGS. 5, 10, 15, 20, and 25 showsuch an arrangement. Each of the laminations may be formed accordinglyso that when they are stacked to form the sheet, the desired shape isachieved. FIGS. 15, 20, and 25 show such an arrangement where each ofthe laminations of the sheet has teeth with a cross section such thatwhen stacked to form the sheet, the teeth have a composite trapezoidalcross-section. Other geometries are also possible. For instance, alamination may be formed with teeth or surface features on the innerlayer as shown in FIG. 33 having an aerodynamic shape to act like acooling fan to draw air directly through the motor.

Adjacent the motor teeth 121, a plurality of pockets or recesses may beprovided in the top surface of the sheet to form one or more sensors fordrive components of the motor. The pockets or recesses may be formed asteeth, for instance, for an encoder and/or for a sensor generatingcommutation signals for the drive of the motor. The pockets or recessesmay also be formed to hold magnets or other devices used in sensors forpositioning functions associated with the drive of the motor. It is notnecessary that each sheet have encoder teeth or commutation teeth orpockets comprising sensors for positioning or for identifying platensegments. A sheet as described herein may include any one or number offeatures depending upon the application. Preferably, the pocket orrecesses are formed in the same manufacturing set-up to reducevariation. The top surface plurality of pockets and recesses may beformed adjacent the plurality of slots forming the motor, and extendparallel to the width of the sheet and spaced along the length of thesheet.

Preferably, the slots in the sheet (or the individual laminations)comprising the motor teeth, and the plurality of pockets and recessescomprising the teeth and pockets used for the encoder, commutation,and/or positioning functions, are formed through a photo-chemicaletching process. The pockets, for instance, forming the encoder trackand/or the commutation track, may be formed by a “partial one sidedetching” or “step or blind hole etching”. This process has provensatisfactory for creating small precise features. As an example, theencoder and commutation track have teeth that are etched to a depth ofapproximately 0.25 mm. Preferably, each sheet forming a platen segmentmay have its features dimensionally identical to another sheet, so thatwhen multiple platen segments are arranged together, each platen segmentwill have the same electrical or commutation angle offset therebyfacilitating set-up and interchanging component parts.

For forming the slots in the sheet (or the individual laminations)comprising the motor teeth, “a single sided through etch” or “doublesided through etching” may be employed to create the slots in thelaminations, although a “double sided through etch” process ispreferred. When photo chemical etching is from only one side there areinherent limits to the size, depth, shape and quality of the features.The “double sided etch” process etches the same feature in both sides ofthe sheet (or lamination) at the same time. Double sided etchingminimizes problems from “over-etching,” creates more accurate and morerepeatable features, and allows different patterns to be etched on eachside of the sheet (or lamination). For instance, “double sided etching”allows forming a tooth that is wider on the bottom than on the top. Theeffect is to create a “trapezoidal” shaped tooth which has bettermagnetic flux properties. For instance, in a trapezoidal tooth shape,the tooth bottom is larger which allows for improved overall flux flowand the top of the tooth is optimized for the motor primary or forproperly saturating of the tooth surface. A two sided photochemicaletching process facilitates this process where one slot can be madelarger than the other leaving an approximate trapezoidal tooth shape. Asdiscussed above, this results in motor teeth that are narrower on thetop side 114 of the sheet and wider on the bottom side 116 of the sheet.Preferably, a combination of “partial one sided etching” and “doublesided etching” is used to form the slots/teeth in the sheet and theencoder track, commutation track and/or other tracks and features in onestep-up, thereby allowing the etched pockets and recesses to align tothe motor teeth as necessary to allow an accurate and repeatable system.Proper implementation of the commutation track and other tracks asdescribed herein requires that the relationship between features and themotor teeth be very repeatable over each pole pitch. Thus, a“combination etch” combines the “double etch” process, which forms largemotor teeth, with a “partial etching” process, which forms the smallercritical features, i.e., pockets for the encoder and other sensorfunctions. The “combination etch” lowers the cost to manufacture thesecondary and synchronizes the motor teeth with the encoder and othersensor pockets. The recessed bridge features may also be formed througha “combination etch” process where the slots forming the motor teeth areetched from the top and bottom while the areas on either side of thebridges are etched from the bottom. Other methods of forming the sheetwith the features described herein may also be used, including EDM orconventional machining.

Encoder Track

As shown in the drawings, a first plurality of pockets 130 is formed ina line adjacent the motor teeth. These pockets may comprise an encoderscale for the motor. Tying the spacing of the motor teeth to the encoderlocks or synchronizes the motor pitch to the encoder pitch. Preferably,the encoder pitch is an integer multiple of the motor pitch. This allowsfor accurate sinusoidal motor commutation, as explained below, whichinherently maintains optimum commutation during the course of motortravel across the secondary. As an example, as shown in FIGS. 1 and 26,the sheet has motor teeth arranged with a 5 mm or 10 mm pitch andpockets for providing an encoder scale arranged with a 1 mm pitch.

The encoder system which includes the read head 74 and teeth 130 maycomprise an incremental linear encoder that generates atransistor-transistor logic (“TTL”) output signal in the form of aseries of pulses relative to the amount of movement. The incrementallinear encoder read head 74 reads the series of teeth 130 on the sheetand creates a series of pulses which the drive interprets as fixedincrements of distance. The encoder is typically an inductive orcapacitive encoder and may also provide output in the form ofsine/cosine information. The encoder system may comprise an incrementalencoder with reference pulses and magnetic sensors.

Preferably, the pockets 130 forming the encoder scale are etchedrelatively near to the motor secondary teeth. The pocket width andoverall pocket pitch are preferably made to match the encoder beingused. The encoder pole pitch will typically be about ½ mm to 3 mm,though the pitch may vary as required in an application to provide theneeded speed for the motor, resolution, or encoder air gap. The typicalresolutions of the encoder ranges from ¼ micron to 1 micron. The pocketdepth for each of the encoder teeth may be approximately 0.25 mm. Thisdepth has been found satisfactory as it allows for implementation of the“partial” photo-chemical etching processes that will create accuratefeatures without degradation. An encoder scale formed in this manner isresistant to mechanical damage and the magnetic fields from the motorand from the magnets in the secondary, and impervious to dirt, oil, andother environmental contaminates.

Commutation Track

In addition to, or in the alternative, a plurality of pockets orrecesses 140 on the sheet may also form a sensor operatively connectedto the drive of the motor to facilitate commutation of the motor. Forinstance, the pockets forming the sensor for the commutation function ofthe drive may be formed in a distinct track(s) in the top surface of thesheet adjacent to or alongside the pockets forming the sensor for theencoder. The sensor may read the teeth in the track and controlcommutation of the motor. Thus, the commutation functionality may beprovided without using Hall Effect sensors or performing a “phasesearch.” Preferably, the pockets used for the commutation function formteeth having a width equivalent to the width of the teeth of the encodertrack. As shown in the drawings, the encoder track 130 and a commutationtrack 140 are in close proximity to each other. Generally speaking, thespacing of pockets or teeth 140 used for the sensor for commutation isthe same as the motor teeth 121, i.e. the same pitch. The pitch of theteeth of the commutation track is preferably at least the same as theteeth of the motor secondary but could be less. Additionally, the pitchof the teeth 130 of the encoder scale are an integer multiple of thepitch of the teeth 121 of the motor secondary pitch. Thus, each motortooth will align with an encoder tooth and a commutation track tooth ina repeating pattern all along the length of the sheet of the platensegment. For ease of discussion, the tooth in the commutation track thataligns with the motor tooth will be referred to herein as a “primarycommutation” tooth or pulse 142. The commutation track may be formedwith an addition tooth between the primary commutation teeth. For easeof discussion, the additional tooth will be referred to herein as a“secondary commutation” teeth or pulses 144. The commutation track maybe formed with additional teeth adjacent the primary commutation teeth.For ease of discussion, these will be referred to herein as “marker”teeth or pulses 146.

The commutation pulses 142,144, which may include primary pulses only,or primary and secondary pulses, depending upon the application, allowthe motor to move only to the next commutation pocket or position toestablish motor commutation. Because the commutation pulses 142,144 aresynchronized with the motor secondary teeth 121, the motor drive is ableto locate a commutation pulse in a distance less than or equal to themotor tooth pitch, thereby enabling the motor drive to determine motorphasing. Because the commutation pulse is aligned with the motor tooth,the drive may readily determine its relative location. Because bothteeth are precisely formed, for instance, through the photochemicaletching processes discussed above, the motor and commutation tooth areprecisely aligned, and quick and precise commutation occurs withoutvariations. This eliminates the need of Hall Effect sensors when used onlinear synchronous motors with magnets in the secondary, or the need of“phase searching” to establish commutation for other linear synchronousmotors that do not have magnets in the platen but have teeth instead.

Hall Effect sensors increase motor costs, for instance, additionalcabling and sensors, and increase operational requirements, forinstance, run time when establishing commutation. Linear drive motorswith Hall Effect sensors may be difficult to align or position in themotor primary, and may degrade commutation in a motor if excessivevariation exists in placement of the Hall Effect sensors on the primaryand their associated magnets on the secondary. Providing an encoder andcommutation track that are synchronized optimally with the motorsecondary teeth eliminates these drawbacks.

As an alternative to Hall Effect sensors, “phase searching” may be usedbut may produce unpredictable results. Phase searching may beaccomplished by powering a coil and aligning the coil to a tooth or amagnet. However, this method sometimes produces poor results due to“cogging” in an “iron core” motor or any motor with a predominatelyiron-based primary or when a load is pulling against the motor, forinstance, from a cable track or a heavy load. Particularly, in verticalapplications, it is usually difficult to perform phase searching due tothe gravitational loads. Providing an encoder and commutation track thatare synchronized eliminates these drawbacks.

Because the commutation pulse is synchronized with the encoder trackpulses which are in turn synchronized with the motor teeth, predictableand repeatable commutation is achieved. In essence, a repeating zeropoint is created at every motor tooth because all three essentialcomponents, namely, the motor teeth, the encoder teeth, and thecommutation teeth, are realigned or set to zero at every motor polepitch. This assures correct sinusoidal commutation alignment regardlessof the distance of the relative motion between the primary and thesecondary, or as discussed below in greater detail, regardless ofwhether the move involves traversing several sheets of platen segments.In other words, after commutation is established, the drive need onlyapply the motor electrical or commutation angle offset through theencoder track to any platen secondary. Because the encoder track teeth,motor teeth, and commutation track teeth are synchronized, variation iseliminated, particularly in motors with smaller tooth pitches havingrelatively lengthy travel-distance requirements.

When dimensional variation of the features of the sheets forming theplaten segments is significantly reduced through the manufacturingprocess, for instance, the photo-chemical etching processes disclosed, aprimary may be replaced with another similar primary and/or a secondarymay be replaced with another similar secondary. This reduces issuesoften associated with a relatively lengthy secondary of a sinusoidalcommutated motor where manufacturing variations associated with thelocations of teeth or magnets stacks up and causes an error toaccumulate with respect to the expected phase positions in the drivethat are tied to the encoder scale, and the actual phase positions inthe secondary. The effect of this error is multiplied with motors havingreduced motor pitch as the drive applies phase currents at less thanprecise positions or in a less-than-optimum manner. Because the encoderand motor secondary teeth are linked in an accurate and repeatingpattern, the drive is less likely to lose commutation, and there is lessvariation during long distances of travel or with locations associatedwith small pitch motors. Furthermore, secondaries may be moved andinterchanged indiscriminately between any number of fixed primaries asdisclosed below without having to slow down or stop to “establishcommutation.” There are at least two aspects disclosed here: (i)sinusoidal commutation varies little if at all in any condition, and(ii) once a primary has “established” commutation in a platen inplurality of like platens, it does not need to “re-establish”commutation in another platen.

In the exemplary sheets shown in FIGS. 6-10, 16-20, and 21-26, the motormoves at most 5 mm and receives a commutation pulse with the motorcommutation and electrical or commutation angle offset stored in thedrive. In the sheets of FIGS. 21 and 26, the primary commutation pulses142 correspond to the first tooth in a grouping or series of markerpulses 146 (either 2 to 4 teeth which are shown in the drawing with“II,” “III,” or “IIII”), and the secondary commutation pulse is alone(i.e., not in a group or series), and is read by the drive as acommutation pulse. In sheet of FIGS. 21 and 26, the additional secondarycommutation pulses 144 allow the drive to read a commutation pulsewithin movement of the motor primary of only 5 mm rather than the 10 mmdistance between primary commutation pulses. As explained below ingreater detail, the primary and secondary commutation pulses 142,144 mayalso be used to identify position on the sheet comprising the platen andinformation about the sheet. A primary and secondary commutation pulseis not required on platens having a relative short length to read apulse. The sheets of FIGS. 6-10 and 16-20 do not show secondarycommutation pulses.

In a different application involving cog-free, iron core or permanentmagnet motors, the teeth of the commutation track 140 may be alignedwith magnet slots/pockets 148 of the secondary (rather than aligning theteeth of the commutation track with slots or pockets defining the motorteeth as described above) (FIG. 27). In addition, the magnetslots/pockets 148 may be aligned with a primary commutation tooth 142and a secondary commutation tooth 144 may be added between adjacentprimary commutation teeth to establish commutation in a distancecorresponding to half of a pole pitch (FIG. 27). On motors with magnetsin the secondary, as shown in FIG. 27, a pole pitch is made up of twomagnets. In FIG. 27, the pole pitch is 50 mm and 5 distinct pulses 146between the poles are added to allow phase searching to be accomplishedwithin a fifth of the pole pitch or 10 mm. Thus, the required distanceof movement for commutation is 10 mm. Additional pulses may be added asneeded as pole pitch increases and/or to minimize the distance the motorprimary needs to move to read a commutation pulse. In a cog-free motorapplication as shown in FIG. 27, the magnets may extend through theslots 148 in the sheet, or be disposed in pockets in the sheet.

Track 3

In addition to the encoder track and/or the commutation track, the topsurface of the sheet may have additional tracks 150. As will bedescribed in additional detail below, another plurality of pocketsformed on the top surface of the sheet may be used to form a sensoroperatively connected to the drive of the motor for positionfunctionality associated with the motor. As described hereinafter,“Track 3” maybe used to provide this functionality. The plurality ofpockets 150 forming Track 3 may be formed as teeth at a similar depth asthe commutation and encoder tracks, and used to form a sensoroperatively connected to the drive of the motor for providing “absoluteposition” information about a sheet or platen segment. As discussedbelow, when Track 3 is synchronized with Track 4 and a plurality of likesheets of the platens are arranged end-to-end in an elongated track,“absolute positional” information may be generated for all of the platensegments.

Track 3 may function as a flexible pseudo-absolute encoding system. Theplurality of pockets or teeth 150 of Track 3 may have a pattern that isdifferent from the other tracks but repeats at a different interval, forinstance, using the example above shown in FIG. 26, every 10 mm alongwith the pattern in the commutation track. The sensor(s) associated withthe drive may be configured or enabled to interpret the pulses generatedby the teeth of the commutation track and the teeth of Track 3 as a“packet” of information that provides absolute positioning informationwithin single sheet. For purposes of illustration and not in anylimiting sense, the pulses generated by the teeth 140 of the commutationtrack may be referred to as “index pulses.” The drive system may beconfigured to look at the index pulses from the commutation track anddetermine the location on the sheet of the platen. For instance, asshown in FIG. 26, 10 bits of unique information may be collected in a“packet” between the commutation and the encoder tracks since there are10 pulses in Track 3 between the “primary commutation pulses”, and fromthat absolute position may be established. The packet of information maycorrelate to a value found in the look-up table or the value, or bedetermined from a look-up table or other algorithm tied to a distinctcommutation pulse correlated to that packet of information.

In the example shown in FIG. 26, the teeth 150 of Track 3 correlate withthe teeth 140 of the commutation track and the encoder teeth 130, wherethere is a 5 mm motor tooth pitch, a 5 mm commutation tooth pitch, and a1 mm encoder scale pitch. The 10 mm repeating sub-segments in thecommutation track are defined by the first pocket or the “primarycommutation pulse.” In the drawings, the primary commutation pulsealways has another index pulse (i.e., marker tooth or teeth 146)associated with it. There may be 1, 2, or 3 teeth next to the primarycommutation pulse to provide the index pulse. This creates a largerrepeating pattern in Track 3 and enables creating more pulses fordevelopment of a large skew or a 10 bit digital word.

In this way, the number of marker teeth 146 next to the primarycommutation pulse 142 may be used to identify a location within a singlesheet. For instance, one pocket next to the primary commutation pulsesegment indicates the position is in the first third of the sheet. Twopockets next to the primary commutation pulse indicate a position in themiddle third of the sheet. Three pockets next to the primary commutationpulse indicate a position in the last third of the sheet. The use ofmarker teeth or pulse after the primary commutation pulse adds amultiplying factor of three to the “packet” of information collected bythe sensors associated with the Track 3. This also reduces the distancethe motor primary moves to find absolute position when many sheets arestrung together. As discussed above, the commutation pulse between theprimary commutation pulses is the secondary commutation pulse. Unlikethe primary commutation pulses, the secondary commutation pulse 144preferably does not have a marker pulse associated with it. Thus, thesecondary commutation pulse 144 is easy to identify in the commutationtrack and is used for commutation only, and not for identifying therepeating pattern in Track 3. The secondary commutation pulse may beeliminated if moving the motor primary a greater distance to establishcommutation is not an issue in the application.

The 10 bits of information found in Track 3 allows for encoding of asheet of a platen segment. As an example, a sheet forming a platensegment having a length of 2500 mm would be sub-divided every 10 mm into250 sub-segments each with its own reference encoding in the mannerdescribed above. Thus, the motor may find absolute position by moving nomore than two primary commutation pulses. Using the example describeabove, the motor may move less than 5 mm to read the presence of acommutation pulse in Track 2. For instance, if the drive reads a primarycommutation pulse, the drive will first establish commutation andcontinue to move until it reads at most 10 bits of information in Track3, thereby enabling the drive to identify its exact location on thesheet. If the drive reads a secondary commutation pulse first, the drivewill establish commutation, advance to the primary commutation pulse,and then read the 10 bits of information in Track 3, thereby enablingthe drive to identify its exact location on the sheet. Because theinformation in Track 3 is synchronized or tied to the commutation pulsesof Track 2, the drive is able to distinguish between and preciselylocate positions for 250 or more unique “home” locations in a singleplaten segment. These “index pulses” establish quick and accurate motorcommutation and absolute position within a platen segment. Because thecommutation pulses in fact function as homing or index pulses within theencoder, the motor's position is very accurate and repeatable to 1encoder count. Therefore, the information from Track 3 applied to acommutation pulse will be accurate and repeatable to 1 encoder count.

Only 7 bits of the 10 bits of information in Track 3 are needed to giveabsolute position in a 2500 mm long sheet. Utilizing all 10 bits wouldallow encoding a 30,720 mm platen. Thus, a flexible pseudo-absoluteencoding system may be used for: (i) minimizing search distance toestablish absolute position; and/or (ii) maximizing the possible platenlength through a plurality of segments. For example, in a motor having afixed primary and moving secondaries having a length of approximately 24inches (610 mm), a 5 mm pitch motor without secondary commutation pulsesis able to find commutation and absolute position in only 5 mm oftravel. The platen may be divided into 4 zones by adding 1, 2 or 3pulses after the primary commutation pulses in the commutation track(Track 2) (see FIG. 26). Track 3 of such a motor may have 5 bits ofinformation and with the 5 mm motor pitch, the motor may be providedwith 640 mm of encoding.

A skew may also be incorporated into Track 3 to provide an alternatemeans of determining absolute position on a sheet of the platen.Accordingly, the “packet” is not 10 bits of information but a skew.There may be a unique skew between each primary commutation pulse or“home” index pulse. Depending upon the application, adding 1, 2, or 3pockets after the primary commutation pulse, as described above, may notbe necessary. One pocket after the primary commutation pulse may be usedto establish position markers in the sheet as shown in FIGS. 21 and 27.Alternately, the secondary pulse may be eliminated if a longer distanceto establish commutation is acceptable in the application. This may beuseful to minimize the programming in the drive.

Track 4

In addition to the encoder track and/or the commutation track and/orTrack 3, the top surface of the sheet may have additional tracks. Aswill be described in additional detail below, another plurality ofpockets formed on the top surface of the sheet may be used to form aflexibly programmed sensor operatively connected to the drive of themotor. The teeth may be formed in a track. As described hereinafter,“Track 4” 160 maybe used to provide “homes” and/or positional limitinformation, and/or platen segments identification.

Magnetic material may be added later into the pockets 160 of Track 4 toform the sensor for setting positional limits. These additional pocketsmay be etched alongside or adjacent to the encoder scale to a depth thatmakes the magnets approximately flush to the encoder scale or as neededto be optimally read by the encoder head. Index pulses from thecommutation track, may be used in connection with the magnetic signalsfrom the positional limits to provide precise and accurate positionallimits for the motor. In general, a magnetic limit may not be veryaccurate or repeatable because of inherent hysteresis. However, theeffects from hysteresis may be eliminated when the magnet positionallimit is used in connection with index pulses from one or both of thecommutation track and/or encoder track. For instance, a pocket forming asensor for a positional limit may comprise a “south” magnet, and whenthe drive receives the signal generated by the “south” magnet, it willassign a position to the motor primary to that of the nearestcommutation index pulse read by the encoder, thereby establishing anaccurate to “home” for the primary. Accordingly, the commutation pulseis in essence a “home” index pulse. Thus, the combination of the magnetand the index pulse provides an accurate and repeatable “latch” forhoming which is accurate and repeatable to 1 encoder count. Also, a“north” magnet may be added to Track 4. The drive may be configured toread the “north” magnet as a limit, as needed by the application. If ahome is not needed, for instance, when the scale is configured as apseudo absolute encoder for a single secondary, as stated above, the“north” and “south” magnets can be simply read as left and right limits.

Alternately, the pockets with magnets or other markers in Track 4 mayalso be used to identify a platen among many platens. Because the drivemay determine the absolute position information for the platen segmentfrom the information from Track 3, the drive may determine where everymagnet pocket is located with respect to every primary commutation pulseand be configured to determine the patterns of the magnets to determinea platen segment's identity. Number codes may be etched into the platensegment to assist in identifying a platen segment from among many. Thisallows for flexible programming. As shown above, the informationcontained in Tracks 2 and 3 establish both commutation and absoluteposition within a single platen segment. A pattern of magnets at thebeginning of a platen segment in Track 4 may also be used to identifyplatens. For instance, “north” magnets may be used to identify a platen,thereby allowing “south” magnets to be used as limits. As analternative, “north” and “south” magnets may be used to identify platensegments. As yet another alternative, where more platens are seamedtogether, a skew may be used in placement of magnets. By way of example,Track 4 may be formed with 200 to 500 magnet pockets in one 2500 mmplaten segment, and by placing a magnet in a different pocket among the200 to 500 available magnet pockets in Track 4 of the platen, one magnetcould be used to identify some 200 to 500 platen segments. By using“north” and/or “south” magnets, 400 to 1000 platen segments may beidentified. If more platens need to be identified multiple magnets maybe used. Magnets may also be added between every primary commutationpulse to reduce the length of travel during identification of a platenfrom the length of the platen segment to only 10 mm in the examplesdescribed above. Magnets may be placed in a repeating pattern in anymultiple of the repeating 10 mm pattern between primary commutationpulses. Additionally, different combinations of “north” and “south”magnets may be used to identify the platens. The information within apattern may be read as a skew or as a digital word. The word could be ina “binary” format with two conditions reading a “north” or “south”magnet providing a “bit” of information. The word could also be in abase 3 format so within a single pocket in Track 4, there can be threeconditions, for instance, a north magnet is read as “+1”, no magnet in apocket is read as “0” and a south magnet as “−1”. Accordingly, the drivemay be configured to read the “packets” of information from the magnetsin Track 4, and access a look-up table to identify the platen segment.Providing Track 4 in a digital word format may be preferred whenconfiguring platen segments as moving secondaries to be passed betweenfixed primaries. In such an arrangement, the drive may be configured toread the first 10 pockets, which may include magnets or spaces, and frominformation identify the platen. In a base-2 system, 1024 platensegments may be identified; in a base-3 system, 59049 platen segmentsmay be identified. Using the principles described herein, the drive ofthe motor may be configured to operate in an “open loop” mode until itreads any commutation pulse in Track 2 whereupon commutation isestablished, and thereafter, the drive may be configured to operate in a“closed loop” or “servo mode”. Elaborating on the example providedpreviously, the drive may also be configured such that when it reads aprimary commutation pulse 142, it establishes commutation, anddetermines absolute position in the platen segment based upon thecombination of the primary commutation pulse of Track 2 and the 10 bitsof information read from Track 3 between primary commutation pulses. Thedrive may also be configured such that when it reads a secondarycommutation pulse 144 before the primary commutation pulse, the driveestablishes commutation at the secondary commutation pulse, advances tothe next primary pulse, and determines absolute position in the platensegment based upon the combination of the primary commutation pulse ofTrack 2 and the 10 bits of information read from Track 3. The drive maythen be configured to move the motor in such a way that the drive readsthe information of Track 4 and then determines platen identity, forinstance, by grouping the Track 4 information into the appropriatepackets defined by the repeating pattern of markers on Track 4, and/orby comparing the information with an algorithm or look-up table. Inother words, the drive is configured to determine absolute position on asingle platen based upon the combination of commutation pulses of Track2 and the information of Track 3. Once absolute position on a singleplaten is determined, the drive may be enabled to read informationencoded in Track 4, for instance, read and interpret any combination ofmagnets and/or spaces present in Track 4. Thus, through the combinationof commutation pulses of Track 2, positional information from Track 3,and the arrangement of markers in Track 4, determine platen identity,home positions or limits. Accordingly, the positional or identificationinformation developed from the combination of the commutation pulses ofTrack 2 and the information of Track 3 and/or Track 4 will be accurateand repeatable to 1 encoder count.

The description above utilizes a sensor comprising magnets installed inthe pocket. However, the sensor may use labels read with an opticalscanner. The pockets 160 may be etched with the label or in a manner tolocate the label instead of the magnets as described above. For example,the instructions may provide programming for the drive to move the motorthrough a sequence of moves. In this way the platen may be used in CNCmachining center, and the instructions encoded in Track 4, may enablethe system to move the platen to a position for a machining operation(i.e., “go to a point and wait for a hole to be drilled”) and thenadvance to the next step. Another application may involve a conveyorline used to feed, position, sort, and/or transfer randomly “movingsecondaries” in a non-sequential manner from a fixed primary to aconveyor and then to another fixed primary capable of rotation to allowtransfer of the secondary to other conveyor lines. Because theelectrical or commutation angle offset may be set for specific motors,there is interchangeability between primaries, secondaries and drivesfor a given motor, and the ability to pass identical secondaries fromone primary to another. The systems and methods described herein mayalso be used in systems in a warehouse or factory with lengthy runs ofconveyor or rail system. In one example, a warehouse may use severalsheets forming platen segments that are installed in a floor of thewarehouse. Also, multiple “robots” may be used on the different sheetsof the platen segments, the positional limits and “home” of each sheetmay be established so that the robots do not interfere with each other.

A linear stage as described herein is highly integrated and merges (i)key motor secondary components, such as motor teeth, encoder teeth,commutation tracks, absolute position tracks, limits and home positions;(ii) a bearing rail system; and (iii) key motor primary components, suchas motor teeth, coils, encoder; all in close proximity to each other andin many cases in a functional interrelationship.

Additional Primary Stage Embodiments

A primary stage may have additional features. These features mayinclude: (i) a bilaterally symmetric three-point roller bearingplacement system on the primary stage; (ii) solid steel stacks; and(iii) an extruded housing, all of which combine to allow for a highlyintegrated and compact design for the primary. When combined with theintegrated motor secondary platen described above, the two create acompact and highly integrated stage. Each feature has advantages. Forinstance, the bearing system described herein lowers bearing materialrequirements and minimizes deflections in a thin motor secondary. Thefeatures of the platen described in the parent applications allows forthe reduction of housing and bearing requirements by integrating themotor secondary, the encoder scale, and the top and side bearings rails.The bearing system may comprise a three-point bearing system on ahousing shown in FIGS. 28-29 and 44-47. A bearing system may also beinstalled directly on the stack as shown in FIGS. 30-31 or embedded in asolid steel stack as shown in FIGS. 37-43. Solid steel stacks providestructural strength for such a bearing system. A solid steel stack maybe provided with mounting attachments for bearings. The bearings may bemounted to projections extending from the stack or embedded withinrecesses in the primary stage or stack. Solid steel stacks also allowthe machining of contours and other features that provide an improvedstack configuration for a primary of a linear drive motor. A solid steelstack may be provided with contouring around the stack to support and toprotect the windings of the stack. A solid steel stack may be providedwith cooling passages for the liquids and to provide cooling as needed,for instance, in high vacuum applications or other applicationsinvolving high speeds, high torques, high motor duty cycles, and/orother applications where the primary develops excessive heat. A solidsteel stack may also use a gas bearing as shown in co-owned U.S. Pat.No. 7,566,997, the disclosure of which is incorporated by referenceherein. A solid steel stack will not degrade under high vacuum andtherefore is advantageous to a stack comprising laminations that maydelaminate over time in such an application. A solid steel stack neednot have any specific epoxy requirements. Accordingly, a solid steelstack may be potted with an epoxy that is specific for the application,i.e., a highly corrosive or an environment where outgassing is aconcern. A solid steel stack may also be potted with epoxy that isappropriate for clean room application, for example. Alternatively, asolid steel stack does not need be potted with epoxy because it is notneeded for support in the stack. A solid steel stack may be used in astand-alone configuration, i.e., housingless as shown in FIGS. 30-31 and37-44.

The stack may also be used in a housing as shown in FIGS. 28-29 and45-55. An extruded housing allows for a platform that with conventionalmachining techniques provides mounting surfaces and alignment of all thecritical components, main roller bearings, stack assemblies, amultifunction encoder, a side rail guidance system, a magnetic preloadassembly, and EMI cavities for power and encoder cable connections. Anextruded housing allows for the creation of multiple mounting surfacesfor critical components, allows for the critical components to bemounted via conventional means, i.e., bolt-on, snap-in, and allows forthe critical components to self-align with each other in the housing insuch a way that the entire primary mates accurately with the variouscritical surfaces on the platen secondary, such as those discussed inthe parent application, including the two main bearing surfaces, theside guidance bearing surface, the encoder scale, the secondary motorteeth, the limits, and homes.

The parent applications described a motor secondary which has a set orsynchronized relationship between the platen and encoder teeth which inturn sets the electrical angle for all secondaries. The disclosure whichfollows describes synchronizing components of a primary to fix theelectrical angle in the motor primary though precise control andplacement of the stack assemblies and the encoder read head. A stack andhousing may have its critical features machined in one setup to reducevariation, and thus, the electrical angle of the primary may be set fora given motor type, thereby allowing interchangeability of variouscritical components of the linear stage and the use of multiple movingsecondaries over a single primary and/or multiple primaries over asingle secondary, as well as combinations thereof. This is particularlyadvantageous in applications where a plurality of moving secondaries arepassed over a stationary primary, and the problems of having tore-commutate for each secondary are eliminated as described in theparent application. For instance, in the housing, locators for theencoder read head may be formed in the same setup as stack locators,thereby allowing a greater repeatability and accuracy during themanufacturing process. Because the electrical angle for all primariesand secondaries are the same, various critical components of the linearstage may be interchanged without having to modify the drive settings,thereby making it very easy for an end-user to install, repair orreplace a motor primary, secondary or drive, and sub components such asthe main or side bearings or encoder heads, etc.

A solid steel stack as described herein may be formed from a low carbonsteel, which has been annealed to enhance magnetic properties. Annealingpromotes magnetic permeability and lowers wattage loss due tomicrostructural change and helps by relieving internal stresses. Thesteel stack may be annealed in a regular atmosphere without concerningabout surface oxidation. Because the stack is machined after annealingto a depth larger than the thickness of oxide layer, annealing may takeplace in a regular atmosphere without concern about surface oxidation.

Eddy current losses may also be reduced by increasing the pole pitch ofthe primary stage. Increasing the pole pitch reduces the frequencyproduced in the coils and thus eddy current losses which are related tothe number of coils and the frequency passing through the coils. Whileincreasing the pole pitch can substantially reduce eddy current losses,increasing pole pitch tends to increase cogging in the motor. Anynegative effects from cogging may be substantially reduced by shiftingtwo teeth with the stack assembly to be misaligned or skewed withrespect to the corresponding platen teeth. Unaligning of the teethwithin a stack assembly of the primary is disclosed in U.S. Pat. No.7,230,355, the disclosure of which is incorporated by reference herein.An integrated stage using an extruded housing and solid steel stack withunaligned teeth, assists in diminishing motor cogging. By selectivelychanging the alignment, one can customize a motor as described hereinwith an amount of acceptable cogging without sacrificing force output.The solid steel stack also enables cooling ports to be more effectivelymachined in the stack. Cooling of the stack assembly may become morecritical with higher speed, higher force and/or higher duty cycleapplications.

As mentioned earlier, FIGS. 30-31 show embodiments of a primary stagecomprising solid steel stacks 62. FIGS. 37-55 show other embodiments ofa primary stage 200 comprising solid steel stacks 210. Referringspecifically to FIGS. 37-44, the stage 200 has two stacks 210 eachcomprising inner and outer teeth members 212,214 with a magnet 216disposed between the inner teeth of the stacks and a coil 218 extendingbetween the inner and outer teeth of each stack. FIGS. 45-48, 51-55 alsoshow solid steel stacks mounted in a housing to form a stage. Each stackcomprises a generally U-shaped configuration defined by the outer toothand the inner tooth members. The outer tooth member 214 defines an outersurface of a channel 220 in the stack and the inner tooth defines aninner surface of the channel 220 in the stack in which the coil isplaced 218. As shown best in FIGS. 37-44, a ledge 221 may be formed onthe inner tooth member 212 of each stack. The magnet 216 may be locatedagainst each ledge 221. FIG. 30 shows one embodiment with the magnetpositioned toward the “back iron portion” of the stack and FIG. 44 showsan alternate embodiment with the magnet positioned closer to the bottomface of the teeth rather than against the “back iron portion” of thestacks. In the embodiment of FIG. 44, the magnet is centered within thecoil with the coil completely covering the magnet. In the embodiment ofFIG. 44, the channel opening may be formed larger than a width of themagnet 216. Thus, the coil may completely cover the magnet and extendtoward the “back iron portion” of the stack. As a result, the coil tendsto balance and direct the alternating magnetic flux between the innerand outer teeth. Accordingly, a solid steel stack may be machined asnecessary with ledge dimensions, tooth widths, and channel opening anddepth, among other features, to create the desired effects, for example,selecting an amount of un-alignment desired while providing a mountingsurface for the magnet.

While the teeth of the solid steel stack may be aligned together so theymatch the pitch of the teeth of a platen secondary, each ledge may alsobe machined to shift the inner and outer teeth members 212,214 of onestack as desired for un-alignment and an amount of a reduction ofcogging as desired as described in U.S. Pat. No. 7,230,355. Forinstance, referring to FIG. 37, the inner and outer teeth members of theright stack (i.e., right of the magnet) may be shifted, or the inner andouter teeth members of the left stack (i.e., left of the magnet) may beshifted. A shift of 5 to 30 degrees or more of a pole pitch relativebetween the left and right side may be introduced with each stackassembly to reduce cogging. Although the FIGS. 37-44 show un-alignmentassociated with a single stack primary stage, it is also possible tocreate un-alignment in one or more phases of a multi-phase primarystage. For instance, one or more stack assemblies shown in the primarystage of FIGS. 45-47 may be un-aligned to create an incremental skewassociated with the primary stage. By providing a solid steel stack, theledge dimensions may be machined as necessary for desired magneticforces, for instance, as described in U.S. Pat. No. 7,230,355. A tooththickness which is 45% of a pole pitch may be best in certain conditionswhile 40 or 50% may be better at other times. Providing a solid steelstack allows for ready adjustment of ledge dimensions and correspondingun-alignment, thereby providing manufacturing flexibility.

The stack outer teeth may be provided with the projections 70 allowinglocations for mounting of the bearings 72 for the stage (FIGS. 30-31).The projections 70 may have threaded holes 68 that accept shoulderscrews for securing roller bearings to the stack (FIGS. 30-31). Theinner teeth may also have projections 73 to allow for support of thecoil and to minimize the potential for the coil to impinge in the airgap (FIG. 30).

In one embodiment as shown in FIG. 44, the projections 70 on the outertooth can be shaped to direct the magnetic flux towards the outer toothwhile assisting in protecting the coil in the stack. For instance, byforming the outer teeth with projections and the inner teeth withoutprojections, the magnetic flux pattern may be directed more effectivelytoward the outer teeth to reduce velocity variations or velocity ripple.With a transverse shorter inner tooth and a slot with vertical walls,more windings may be incorporated into the coil, and also the magneticcircuit within the stack may be stronger and more balanced. In contrastto a round slot, a rectangular shaped slot enables the windings tomaintain better form around the magnet. A larger, for instance, atransverse longer, outer tooth tends to compensate for any imbalance inthe alternating flux pattern between the inner and outer teeth, byproviding a preferred flux path away from the inner tooth. In otherwords, any unbalance alternation in flux pattern between the inner andouter teeth caused by the coil's interaction with the inner tooth may beovercome by forming the shape of the outer tooth as necessary, forinstance, increasing its traverse length. The solid steel stack enablesthe inner and outer teeth to be formed as necessary for this effect. Theforming process may also include forming variations in the tooth widthsor small projections or contours on the extremities of inner teeth tohelp retain the coil winding in the slot while positioning it near tothe bottom of the tooth.

The stacks may also be provided with internal passages 230 (FIG. 43).The internal passages provide internal cooling for the stacks. Theinternal passages may also be used for a gas bearing for the stage, inwhich case, the discharge port 232 for the gas bearing may be in one ormore teeth of the stack(s) (FIG. 43), or through the epoxy surroundingthe stack or stage (not shown), where the gas is discharged against theplaten surface to form the gas bearing as disclosed in U.S. Pat. No.7,566,997. The discharge ports 232 may also be used to discharge acooling gas on to the platen to cool the stack as well as the secondary.The stacks may also have end user mounting holes 68, for instance, whenthe stacks form a housingless primary stage (FIGS. 30-31). The stacksmay also have mounting holes and/or other locator features to allow thestacks to be mounted in the housing (FIGS. 45-48).

The primary stage 200 of FIGS. 37-42 has the bearing system embedded inthe interior of the stack assembly to provide support to the middle ofthe secondary and to offset deflections caused by high magnetic loadsbetween the secondary and primary. This is of particular concern withlarger force, slow moving primaries with large pole pitches and/or widestacks when combined with thinner or weaker secondaries, or where thereis a lack of flatness associated with the secondary or flatness in thesecondary that cannot be tightly controlled. Preferably, a bearingassembly 252 is installed in an interior recess 254 formed between theinner teeth 212 and below or on the ledge 221 to accommodate the bearingassembly. The magnet 216 may be located above the recess 254 and bearingassembly 252. The bearing assembly 252 comprises a low friction,non-magnetic bearing 256 with an axle 262 which is mounted in a saddleportion 258 of a bearing housing 260. The saddle portion 258accommodates the axle 262 of the bearing. The bearing 256, axle 262, andthe saddle portion 258 may be formed from a non-magnetic material suchas stainless steel, brass, bronze, and/or plastic. The bearing housing260 is dimensioned for relative sliding motion up and down (FIGS.37,41,42) inside the recess between the stacks and under the magnet. Inthe alternative, the recess may be formed to extend partially into theinner tooth 212 to accommodate a larger bearing assembly.

Jackscrew holes 266 extend through the ledges 221 into the recess 254.The jackscrew holes may be threaded holes to threadably engage jackscrews 268. To adjust the air gap, the jackscrews 268 may be threaded asnecessary at the top of the stage 200 and the relative position of thebearing assembly 252 in the recess 254 may be adjusted. The jackscrews268 may abut the bearing housing or threadably engage the housing. Thejackscrews may also serve as mechanical stops to maintain the air gapfor instance during the high magnetic preloads, and/or in the event theprimary is subjected to shock or excessive vibration. If the bearingassembly needs replacement, the jackscrews provide a locator to quicklyreestablish the required air gap.

FIGS. 45-48 show an alternate embodiment of the linear drive motorprimary with solid steel stacks 300 assembled with magnets 302 to formstack assemblies 310 installed in a housing 312 made of a non-ferrousmaterial like aluminum. FIG. 45 shows the stack assembly 310 to beassembled with the housing 312. FIG. 46 shows further detail where thehousing 312 comprises an extruded housing. The housing 312 includes amounting surface 314 for the end user application. The housing shown inFIGS. 46-48 has six extruded passageways 315 adjacent the applicationmounting surface 314. The primary stage may be cooled by simpleconvection with ambient air passing through the extrusions as it moves,or, alternately, via pressure source which directs pressurized gas orfluid into one or more of the passageways 315. Preferably, theapplication mounting surface 314 includes T-slots that enable end userapplications to be directly bolted to the housing. While the drawingsshow that the second and fifth passage ways 315 include slots foraccommodating a T-nut for the application mounting surface 314, themounting surface may also include other configurations as required bythe end user. One or more of the extruded passageways, for instance, apassageway adjacent to the encoder, may have openings communicating withthe two EMI shielded accesses for power connectors and the encoder readhead in the upstanding wall 320, thus reducing cabling and connectorrequirements, and providing for cable management.

The housing comprises a stack mounting support surface 316 which isgenerally horizontal and arranged parallel to a platen of a secondary.The stack mounting support 316 includes locators 318 for mounting thestacks. The locators 318 on the stack mounting support may includemounting holes. The stack mounting holes (i.e., locators) 318 on thehousing correspond to mounting holes 319 on the stack top surfacethereby enabling the stack assemblies to be bolted directly to theextruded housing. In this way, the stack mounting holes may be precisiondrilled locators. The stack mounting surface locators may include otherfeatures including precision machined dowel pins, recesses or otherkeyed arrangements that allow the stacks to fit in a precise manner onthe stack mounting surface. FIGS. 45-48 show locators 318 for mountingthree stack assemblies 310 on the stack mounting surface. It should beappreciated that more or less may be used depending upon the applicationand the number of phases incorporated into the motor. For example, inthe case of 3-phase motors, 3 locators for 3 stacks may be used for a“2-pole motor” (FIG. 45), or 6 locators for 6 stacks may be used for a“4-pole motor” (FIG. 49), the “4-pole motor” providing about twice theforce. In another example, in the case of stepper motors, 2 locators for2 stacks may be used for a “2-pole, 2-phase motor,” or 4 locators for 4stacks for either a “4-pole, 2-phase motor” or for a “2-pole 4-phasemotor”. An advantageous means to skew the locators will be disclosedlater.

The housing has upstanding wall members 320,322 extending transverse tothe stack mounting support 316 and defining longitudinal sides of thehousing. The terms left and right will be used for ease of illustrationin referring the housing shown in FIGS. 44-47 and is not intended to belimiting in any way. The wall members (reference character 320 indicatesthe right wall member and reference character 322 indicates the leftwall member) provide mounting locations for bearings. The left and rightside wall members have flat surfaces 320A, 322A which are perpendicularto the upstanding walls 320, 322 and parallel to the stack assemblysupport surface. The left side wall member 322 includes forward and aftbearing locators 324,326 for forward and aft bearings 328,330. The leftside wall member flat surface 322A also provides a locators 332 for theside guide roller bearings 334, and locators 336 for the magneticpreload assembly 338 between the side guide bearing locators. The rightside 320 wall member includes a centralized bearing mount locator 340for a central bearing 342. The right side wall member 320 also includesan encoder read head locator 344 for an encoder read head 346. Theencoder read head locator may comprise a ledge formed in the upstandingwall member 320. The encoder read head locator is preferably formed inan EMI shielded access in the housing. By providing an EMI shielding inthe access with the encoder read head locator, the requirements for theencoder housing and the encoder cabling may be reduced andelectromagnetic interference from other motor components may be reduced.The right side wall member 320 includes an access recess 348 forconduits 350 that direct pressurized gas into the housing 312 and/or thestacks assemblies 310 for cooling, and also depending on the applicationto form a gas bearing for the primary (not shown). The access recess 348may also house wires and power supplies to the stack assemblies, inwhich case the access recess 348 may be shielded to preventelectromagnetic interference with other motor components, i.e., theencoder. By providing an EMI shielded access recess, the requirementsfor shielded power supply connectors are reduced. The access recess 348may communicate with one or more of the extruded passageway 315 in thehousing for cable management and routing to other components asnecessary.

Because the top surface of the stack (i.e., the surface of the stackopposite the teeth) is flat and in direct contact with the housing viathe stack mounting surface and locators, there is good thermal contactbetween the two and any excess heat generated by the stack may bedissipated through the housing. For instance, a plate with a coolinghose attached to a nipple extending through the plate may cover the endof a passage way 315 to allow cooling fluid to be directed through theextruded passageway. In a similar set-up, cooling fluid through acooling hose may be directed into the extruded passageway and then tothe stack assemblies and other components as necessary. For instance,ports 351 in stack mounting surface 316 may be brought into registerwith stack ports 351A machined in the stacks when the stack assembliesare mounted in the housing. When the stack assembly is mounted on thestack mounting surface, a fluid tight connection may be formed. Forinstance, O-rings may be installed in the ports and the stack conduitsto create a fluid tight connection. Thus, the passageways in the housingmay communicate directly with the stack conduits for cooling. As anexample, in a vacuum or very high force and/or duty cycle application,the second or third extruded passageway and corresponding set of portsmay be arranged to deliver influent cooling fluid to the stackassemblies, and the fourth or fifth extruded passageway andcorresponding set of ports may be arranged to receive the effluentcooling fluid from the stack assemblies. Alternatively, for example, agas, may be passed through the extruded passageways and into the ports351 to enter the stacks and be discharged onto the platen, for instance,to establish a pressurize gas bearing. A threaded orifice may be addedas needed to control the gas flow. In addition, with this arrangement,the cooling fluid (i.e., gas) not only cools the solid steel stack butalso cools the secondary. Generally speaking, the carbon content in thematerials forming the secondaries tends to increase heat generation.Although the secondaries described above have in general a lower carboncontent due to their construction, and particularly, their thinnerlaminate construction material (0.06%-0.08% carbon content as comparedto 0.18% typically found in the thicker secondaries used on other linearmotors), directing pressurized cooling fluid through the stack and ontothe platen is an effective means for cooling of the secondary.Alternatively, one or more of the extruded passageways may be renderedfluid tight to provide the desired path of cooling fluid flow throughthe primary and associated components. Alternatively, cooling fluid mayflow through the housing passageways adjacent to the stack locators andprovide cooling for the stack assemblies by the action of heat transferthrough the stack mounting surface 316. Alternatively, cooling fluid maybe flow from its source directly into the passageways 315 rather thanfrom access 348 in any one of the methods described above. The coolingfluid may be liquid or gas.

The encoder read head locator 344, stack support surface 316, and stackmounting locators 318 are preferably machined and/or formed in thehousing in a single setup to minimize variation and to synchronize(i.e., lock in) the electrical angle for the primary. Flat surfaces320A,322A, and the side guide bearing locators 332 and/or magneticpreload assembly locators 336 may also be machined in the same set-up tominimize variation. Likewise, the bearing mounts 324,326,340 on the leftand right upstanding wall members 320,322 may be machined in the sameset-up to minimize variation. Thus, the flat surfaces 320A,322A arepreferably parallel with stack assembly mounting surface 316. Theencoder read head locator, central bearing mount, and forward and aftbearing mounts have mounting surfaces that are perpendicular to flatsurfaces 320A,322A. The encoder read head locator, central bearingmount, and forward and aft bearing mounts have surfaces that areparallel to each other. All the critical dimensions for the primarystage are formed in one set-up thereby minimizing variation andproviding accuracy and repeatability. In particular, because this methodenables to the locators for the stacks, bearings, magnetic preload, andencoder to be formed with precise requirements for parallelism andperpendicularity, these critical components for the primary may beself-aligned by simply bolting them on and assembled onto the housingwith lower requirements. In particular, the bearings will track properlyand accurately on the platen thus reducing wear on the platen.

In summary, an exemplary housing as formed using the methods describedherein allows for precise setup of seven critical bearing and stackmounting surfaces in four distinct planes. For example, the extrudedhousing 312 is arranged with left and right upstanding wall members320,322 standing vertically. The upstanding wall flat surfaces 320A,322Aalong with the stack mounting surface 316 are machined, for instance,with a bottom of an end-mill, making them parallel to each other andcreating a reference plane for subsequent operations. This allows theside guide bearings 334 to roll flat and perpendicular to the side faceof the platen. Next, the forward and aft and central bearing mountingsurfaces 324,326,340 are machined with the side of an end-mill. Thisallows the main bearings 328,330,342 to travel parallel to each otherand also to travel flat on the two main bearing surfaces. Next, the sideguide bearing locators 332 and magnetic preload assembly locators 336are formed by drilling and tapping holes. Thus, the two side bearings334 and the main bearings 328, 330,340, as a group precisely travel ontheir respective bearing surfaces relative to the platen withoutintroducing a skew or un-parallel motion in any of the three bearingsurfaces which would cause premature bearing wear and failure. Then, thestack assembly locators may be formed by drilling mounting holes 318into the housing. The encoder read head locator 344 may then be formedwith the side of an end-mill assuring that the electrical angle for theprimary is fixed. Any additional adjustment for cogging by “un-aligning”may then be made. A housing made in this fashion eliminates mounting andaligning components and bearings to a conventional carriage.

FIG. 46 shows an exploded view of the housing of FIG. 45. As shown inFIG. 46, the three stack assemblies 310 are mounted on the stackmounting support 316. The encoder read head 346 is received in theencoder read head locator 344. Three bearings 328,330,342 are used toguide the primary and support the high magnetic loads from the stacks.The central roller bearing 342 is inserted in a bearing locator 340 onthe left side wall member 320, and a forward and an aft bearing 328,330are inserted in bearing locators 324,326 on the right side wall member322. The roller bearings 328,330,342 are mounted to the upstanding walls320,322 via shoulder bolts 352 extending through a center or inner raceof the respective roller bearing. An inner diameter surface of therespective roller bearing inner race engages the shoulder of theshoulder bolt. On the right side wall member 320 bearing mount, theshoulder bolt 352 is directed through the inner race of the rollerbearing and into a slot 354 where the shoulder bolt distal end isthreaded into a square nut 356. The square nut 356 is arranged forsliding motion in a keyway 358 behind the slot 354. The keyway 358engages both sides of the square nut and prevents rotation of the squarenut 356 thereby facilitating tightening the shoulder bolt andpositioning the bearing in the slot. Thus, on the right side wallmember, the bearing 342 is positioned on the exterior of the rightupstanding wall member between a head of the shoulder bolt and theupstanding wall. Shims or washers (not shown) may be used to engage thesides of the inner race and to stand the bearing off the upstandingwall. The arrangement on left side upstanding wall 322 is different. Theleft wall forward and aft bearing mounts 324,326 each include anelongated hole 360 through which the shoulder bolt 352 is directed. Theshoulder bolt 352 is then directed through the inner race of the rollerbearing where the shoulder bolt distal end is threaded into the squarenut 356. Given the size of the square nut and its relative position inthe elongated hole, the stack mounting support may be formed with akeyway 362 that engages at least one side of the square nut to preventthe nut from rotation as the shoulder bolt is tightened. Alternatively,a tool or wrench, may be used to prevent rotation of the square nut whentightening the shoulder bolt and positioning the bearing. Shims orwashers (not shown) may be used to engage the sides of the inner raceand to stand the bearing off the upstanding wall. Thus, on the left sidewall member, each bearing 328,330 is positioned on the interior of theleft upstanding wall member between the square nut and the upstandingwall. Although the drawings show one particular arrangement of thebearings in their respective bearing mounts, certain aspects of one ormore of the bearing mounts may be used at one or more bearing mountlocations as may be desired by the application.

Jackscrew holes 364 extend through each bearing mount 324,326,340. Thejackscrew holes 364 may be threaded holes to threadably engagejackscrews (not shown) for each bearing mount. The jackscrews may beaccessed through an access hole 365 in the application mounting surface314 that extends to each bearing mount 324,326,340. As mentioned before,the jackscrews may be used to adjust the position of the bearing in theslot (i.e., right side bearing location) and/or elongated holes (i.e.,left side bearing location), for instance, for setting the air gap ofthe primary. To adjust the air gap, the jackscrews may be threaded asnecessary at access holes in the application mounting surface, and thenthe three shoulder screws 352 are tightened to make sure that thebearings are pressed firmly against their mounting respective mountingsurfaces 324,326,340. The bearing mount and locator surfaces allow thebearings self-align such that they are parallel to each other, and totheir respective bearing surfaces. The jackscrews may abut the shoulderof the shoulder bolt. The jackscrews may also serve as mechanical stopsto maintain the critical air gap in application involving high magneticpreloads, and/or in the event the primary is subjected to shock orexcessive vibration. The jackscrews enable finely setting andmaintaining minimum air gaps that may be critical in applications whereforce and/or torque is directly related to establishing and maintaininga very small air gap. Furthermore, if the bearing needs replacement, thejackscrews provide a locator to quickly reestablish the required airgap. Thus, downtime from preventative maintenance or bearing replacementis reduced as the mounting screws and bearings are easily assessable,and re-setting of the air gap is either not required or is greatlysimplified.

The side guide roller bearings 334 are mounted by directing threaded endof the shoulder bolt 366 through threaded holes (i.e., locators) 332formed in the horizontal portion 322A of the left side wall member 322.The edge of a bolt or a shoulder bolt 366 engages the inner race of theside guide bearing. Although the side guide bearings 334 may simply bolton to the housing and self-align with the locators 332 as shown in thedrawings, the side guide bearings may be arranged as the central bearingon the right side wall member with a slot and keyway thereby allowingthe use of a jackscrew to adjust each side guide bearings as necessary,in the manner described above.

The housing 312 facilitates manufacturing and final assembly of theprimary stage. The three stack assemblies 310 (i.e., two stacks with amagnet) may be mounted in the housing on the stack mounting support 316using the stack locators 318. Windings 370 (FIG. 46) may then bedisposed around each stack assembly 310. The stacks 300 each haveprojections on the outer teeth that facilitate in protecting thewindings. The stacks 300 may have projections extending from the innerteeth to cover the windings. Alternatively, the inner teeth have littleor no projections so to accommodate a coil with additional windingsand/or to help balance the magnetic circuit as described above. Thewindings 370 may be dropped into position around the stack assembliesand may be in place near the bottom of the tooth and around the magnetas described above. The main load bearings 328,330,342 may be mounted intheir respective mounts 324,326,340 on the upstanding wall members320,322 of the housing 312. The encoder read head 346 may be mounted inthe EMI shielded recess comprising the encoder read head locator 344 ofthe housing with mounting screws and a mounting plate. The side guidebearings 334 may be mounted in their respective bearing mounts 332 onthe left side upstanding wall 332. The magnetic preload assembly 338 maybe installed in its respective mount 336 on the left side upstandingwall 332. The magnetic preload assembly may have slotted mounting holesto allow for adjustment of the air gap between the platen and thepreload assembly to create more or less magnetic attraction, as needed,to maintain the primary against the platen and prevents unwanted yawmotion when traveling along the platen. Power and pressurized gasconnections may be directed through the EMI shielded access recess 348or through the extruded passageways 315. The housing may be then treatedwith an epoxy 380. FIG. 47 shows an embodiment of the primary with epoxy380 extending over the stack assemblies 310. FIG. 48 shows an embodimentof the primary without an epoxy extending over the stack assemblies 310.FIG. 47 also corresponds to the embodiment of FIG. 48 before the epoxy380 is applied.

Although the primary stage of FIGS. 45-48 is arranged with three rollerbearings 328,330,342, other arrangements may also be used. FIG. 49 showsan alternate embodiment of the housing of FIG. 45-48. For the ease ofillustration features common between the embodiment of FIGS. 45-48 andthe embodiment of FIG. 49 have not been indicated in FIG. 49. In FIG.49, the housing 382 has opposite left and right upstanding wall members384,386. The left wall member 384 includes a forward bearing locator 388and an aft bearing locator 390. The right wall 386 member includes acentral bearing load point 391 comprising two bearing locators 392 forapplications involving high magnetic loads between the primary and thesecondary or applications where flatness of the secondary cannot becontrolled. FIG. 50 shows an alternate embodiment of a linear drivemotor 394 with a platen 396 and a primary 398 movable across the platenusing five bearings. The primary 398 has a housing 399 (shown inphantom) with one wall member 400 having locators for a forward bearing402, an aft bearing 404, and a central bearing 406; and the oppositewall member 408 having two bearing locators 410,412. In the embodimentof FIG. 50, the magnetic load assembly locator (not shown) may bedisposed on the wall member 400 between the forward and central bearinglocators 396,400, and/or between the aft and central bearing locators398,400. In the embodiment of FIG. 50, the encoder read head locator maybe arranged on the opposite side wall 402. Other combinations may alsobe used with additional bearings provided at each location dependingupon the application. For example, there may two bearing mounts at eachlocation shown in the primary of FIG. 50. Preferably, the arrangement ofthe bearings on the left and right upstanding wall members is staggered.

Preferably, each bearing load point, whether it comprises two or morebearings grouped together at a particular location on the housing (i.e.,the central bearing 392 of FIG. 49), or a single bearing at a particularlocation on the housing, are on opposite sides of the housing of theprimary in non-adjacent positions. The number of bearings used at aparticular location to create the bearing load point (an odd or evennumber) is not critical. In FIGS. 45-48, the main roller bearings328,330,342 create three bearing load points that are non-symmetricabout the axis defined by the direction of travel of the primary butsymmetric about the axis defined by a direction transverse to thedirection of travel (i.e., bilaterally symmetric). In FIG. 49, the pairof bearings installed in the locator 392 creates the approximate bearingload point 391 on one side of the primary, and the bearings installed inthe forward and aft locators 388,390 each create a bearing load point393 on the other side of the primary. In FIG. 49, the arrangement ofbearing is also bilaterally symmetric. By way of example, the housing ofFIG. 49 includes 3 additional stack locators that may be used to providean additional pole. The additional pole creates additional magneticforce between the primary and secondary. The additional bearing at thebearing load point 391 is used to counter the added magnetic loading.Similarly, the added bearing may be used at the bearing load point 391(or any other bearing load point) to counter greater end user payloadsfor the motor. Similarly, in FIG. 50, each of the 5 bearings creates itsown bearing load point with the near side wall having 3 bearing loadpoints and the far side wall having 2 bearing load points, preferably,positioned between the 3 bearing load points on the opposite (near side)walls. Thus, the arrangement in FIG. 50 is bilaterally symmetric. Thebilateral symmetric arrangement of bearing load points minimizesdeflections of the secondary and assists in maintaining a critical airgap for the motor. The bearing(s) are moved to the center on one longside of the primary to minimize both the amount of deflections in thesecondary and also the effect of the deflections. With the bilateralsymmetric arrangement of bearings, critical defections in the secondaryare minimized by inducing double bending stresses into the platen andmotor housing rather than single bending stresses. In a bilateralsymmetric arrangement of bearings, deflections in the primary housingand/or secondary platen caused by high magnetic loading between theprimary and second may be minimized thereby assisting in maintaining acritical air gap. In turn, the secondary may be formed from thinnerlaminate construction as described before, and the motor may operatewith a smaller air gaps and achieve greater force and morefunctionality, for instance, through a plurality of moving secondariespassing over an inverted primary. In an application involving aplurality of moving secondaries passing over an inverted stationaryprimary, the secondary is preferably a relatively thin member to reducethe mass that the primary is moving. In comparison to a bearing systemwith bearing load points on the corners of the housing of the primary,the bilaterally symmetric bearing system allows for a stable air gap atvery small air gaps, an increase in motor force, an increase in motorreliability, and a reduction in the weight of the motor.

FIG. 49 also shows forming the locators for the stacks in a manner toachieve a desired amount of “un-alignment.” The housing 382 may beformed such that the relative position of the first set of stacklocators 318A (i.e., forward 3 pairs) is skewed from the second set ofstack locators 318B (i.e., aft 3 pairs) relative to a tooth pitch on acorresponding secondary. Thus, the inner and outer teeth of the stacksin the second set of stack locators may be shifted relative to the pitchof the teeth of the platen secondary to reduce cogging. As mentionedbefore, the arrangement of stack locators 318A,318B may be used inconnection with a 3 phase, “4-pole motor.” The housing shown in FIG. 49illustrates scalability with the provision of a longer housing toaccommodate additional stack assemblies for added phases or poles.Alternately, magnetic imbalance may be compensated for by inverting thephasing on the each of the phases in successive poles and then shiftingthe stack locators in the housing by 180 degrees. By reversing thepolarity of a set of coils in a successive pole, non-linearities in fluxmay be compensated.

FIGS. 51-55 show an alternate embodiment of a primary stage 420 for alinear drive motor where stacks 422 of the primary stage compriserectilinear cross section members formed from solid steel. The solidsteel stacks 422 may have a central opening 424 to accommodate a coilwinding 426 and mounting surfaces 428 for attachment of the stack to ahousing 429. The mounting surfaces 428 may comprise a threaded hole toallow the stack to be bolted in the housing 429 as shown in thedrawings, and/or other locators, for instance, as described in theprevious embodiments. A magnet 430 is disposed between two like stacks422 to form a stack assembly 432. FIG. 51 shows the stack assembly withthe stack in a semi-finish state. FIG. 52 shows the stack assembly inthe housing in a finished state. FIG. 53 shows the stack assembly in thehousing in a finished state with coil windings inserted in the stacks.

In one method of constructing the primary stage, stack assemblies 432(i.e., stacks with a magnet disposed therebetween) having semi-finishdimensions may be mounted in an interior portion of a housing 434 usingthe stack locators formed in the stacks 428 and the housing, forinstance, mechanical fasteners 436. The stacks and locators mayincorporate any one of the aforementioned features. Then, the housingwith installed stack assemblies 432 may go through a slotting operationto form a slot 438 in the bottom face of the stack that allows for theinsertion of the coil windings 426 in the central openings of eachstack. The stacks may have semi-finish dimensions that facilitateassembly with the housing as the stacks will be finished machined afterassembly with the housing. Preferably, in the same setup, the housingwith installed stack assemblies may go through a machining operation tofinish machine the stacks, and particularly, finish machine the stackbottom surfaces with teeth 440. For instance, the stack teeth 440 may befinished machined to provide the desired motor pitch, desired amount ofun-alignment to reduce cogging, and skew between successive stackassemblies, as described above. In small pitch motors, a series ofstacks may be finish machined in one setup to produce various stackassemblies with precision formed teeth that may be aligned orun-aligned, as desired, without the need of an optical comparator to setvarious stacks of other phases of the motor and other components in thehousing. The teeth 440 on the bottom face of the stacks may be arrangedas a group in a pattern (i.e., tooth pitch) as necessary on the bottomface of the stack and a group of teeth need not fully occupy the face ofthe stack. For instance, in one embodiment, as shown in FIG. 53, thestacks may have their semi-finish width dimensions made slightly widerthan a width needed to accommodate the number of teeth to be machined onthe bottom face of the stack (i.e., four teeth on each side of theslot). The oversize semi-finish stack width dimension providesadditional material on either side of the stack to facilitate themachining/manufacture of the teeth on the stacks and to allow forunalignment as may be required, and to account for any assemblyvariances. In an application involving a small pitch, the teeth of thestack assemblies may incorporate a skew to produce a stage with minimalcogging, which may be advantageous in low speed applications (i.e.,scanning applications) where smoothness of motion is required. It shouldbe appreciated that the individual stack assemblies may be machined toform skew for unalignment, and then assembled with the housing anoptical comparator to ensure desired positioning.

FIGS. 52,54,55 show the primary stage 420 with the housing 429 havingmany of the features mentioned above. The housing 429 of FIGS. 52,54,55may be an extruded housing with wall members 442A,442B forming mainbearings locators 444, side bearing locators 446, an encoder read headlocator 448, and magnetic preload assembly locator 450. Afterwards, thehousing with installed stack assemblies is machined to finish thefeatures of the stack, the housing may have its other features finishmachined to allow finish assembly of the encoder read head 452, magneticpreload assembly 454, and the main bearings 456, and the side guidebearings 458. The machining of the encoder read head locator 448 assistsin locking the commutation electrical angle of the primary, as mentionedabove. The housing may also include features for jackscrew holes 460,shoulder bolts 462, square nuts 464, a keyway 466, a ledge 468, EMIshielding 470 for the encoder read head access and related electronics,and other power cabling conduits 472 with EMI shielding on an oppositeside (not shown), arranged in the manner described previously. Theprimary may also be potted with an epoxy 474. The motor teeth andencoder read head may use teeth on the secondary similar to thatdisclosed above. Constructing the primary in this way enables all of thecritical components of the primary to be aligned and mated optimally tothe platen, thereby locking the electrical commutation angles for theprimary and secondary.

The primary shown in FIGS. 52,54,55 also includes an internalcompartment 480 for housing a spring member 482. The spring 482 may besized to respond to the weight of the primary and the end user payloadfor use in a vertical application (i.e., a gantry), and depending uponmotor travel requirements, the spring may be sized to compensate for arelatively heavy payload when using a small primary. The spring alsoassists the primary in performing a “phase search” in a verticalorientation when the effects of gravity may otherwise prevent searchingor when a commutation track feature as described above is not enabled inthe drive. The spring may also be used to cushion the motor in the eventof power loss.

The solid steel stack constructed in the manner described above may beused in a single axis motor, or a “dual axis” motor where semi-finishedstack assemblies are mounted in an orthogonal orientation in a housing,and then the housing with mounted stack assemblies undergoes a slottingoperation to enable the insertion of coils in the central openings ofthe stacks and a machining operation to finish machine the teeth instacks in the desired orientation, pitch, unalignment, as describedabove. The machining operation may also include forming holes for a gasbearing as shown in co-owned U.S. Pat. No. 7,566,997.

While certain embodiments have been described in detail in the foregoingdetailed description and illustrated in the accompanying drawings, thosewith ordinary skill in the art will appreciate that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any and all equivalents thereof.

What is claimed is:
 1. A primary for a linear drive motor: a stagecomprising: a first stack having an inner tooth with an interior surfaceand exterior surface and an outer tooth with an interior surface and anexterior surface, the inner and outer teeth being monolithically formedin the first stack, the inner tooth interior surface being spaced fromthe outer tooth interior surface so that the inner and outer teeth forma generally u-shaped cross-section for the first stack, the first stackbeing monolithically formed from a steel, the inner tooth having a toothwidth defined by the inner tooth interior surface and inner toothexterior surface, the outer tooth having a tooth width defined by theouter tooth interior surface and outer tooth exterior surface; a secondstack having an inner tooth with an interior surface and exteriorsurface and an outer tooth with an interior surface and an exteriorsurface, the inner and outer teeth being monolithically formed in thesecond stack, the inner tooth interior surface being spaced from theouter tooth interior surface so that the inner and outer teeth form agenerally u-shaped cross-section for the second stack, the second stackbeing monolithically formed from a steel, the inner tooth having a toothwidth defined by the inner tooth interior surface and inner toothexterior surface, the outer tooth having a tooth width defined by theouter tooth interior surface and outer tooth exterior surface; a magnetdisposed between the first and second stacks adjacent the exteriorsurfaces of the inner teeth of the first and second stacks; and a coilwrapped between the first and second stacks with an inner diameterportion of the coil circumscribing the interior surfaces of the innerteeth of the first and the second stacks and an outer diameter portionof the coil adjacent the interior surfaces of the outer teeth of thefirst and the second stacks.
 2. The primary of claim 1 furthercomprising fluid passages formed in the first and second stacks.
 3. Theprimary of claim 2 wherein the fluid passages cool the first and stacks.4. The primary of claim 3 wherein the gas passages have discharges onthe bottom faces of the first and second stacks.
 5. The primary of claim1 further comprising application mounting holes in a top surface of atleast one of the first and second stacks.
 6. The primary of claim 1,wherein the outer tooth of the first and second stacks each has aprojection extending in a direction that is transverse to the widthdimensions of the outer tooth.
 7. The primary of claim 6, wherein theouter tooth projection is configured for mounting of a bearing for theprimary.
 8. The primary of claim 1, wherein the inner tooth has a lengthalong a direction transverse to the inner tooth width, and the outertooth has a length extending from a direction transverse to the outertooth width, and the inner tooth length is less than the outer tooth andlength.
 9. The primary of claim 8, wherein the coil envelops the magnet.10. The primary of claim 1, wherein bottom surfaces of the teeth arearcuate and conform to a curved secondary of the linear drive motor. 11.The primary of claim 1, wherein the stacks comprise an annealed lowcarbon steel.
 12. The primary of claim 1, wherein the teeth of the stackhave a spacing that is offset relative to a secondary associated withthe primary stage.
 13. A primary for a linear drive motor comprising: astage comprising: a stack assembly comprising: a first stack having aninner tooth with an interior surface and exterior surface and an outertooth with an interior surface and an exterior surface, the inner andouter teeth being monolithically formed in the first stack, the innertooth interior surface being spaced from the outer tooth interiorsurface so that the inner and outer teeth form a generally u-shapedcross-section for the first stack, the first stack being monolithicallyformed from a steel, the inner tooth having a tooth width defined by theinner tooth interior surface and inner tooth exterior surface, the outertooth having a tooth width defined by the outer tooth interior surfaceand outer tooth exterior surface; a second stack having an inner toothwith an interior surface and exterior surface and an outer tooth with aninterior surface and an exterior surface, the inner and outer teethbeing monolithically formed in the second stack, the inner toothinterior surface being spaced from the outer tooth interior surface sothat the inner and outer teeth form a generally u-shaped cross-sectionfor the second stack, the second stack being monolithically formed froma steel, the inner tooth having a tooth width defined by the inner toothinterior surface and inner tooth exterior surface, the outer toothhaving a tooth width defined by the outer tooth interior surface andouter tooth exterior surface; a magnet disposed between the first andsecond stacks; and a coil wrapped between the first and second stackswith an inner diameter portion of the coil circumscribing the interiorsurfaces of the inner teeth of the first and the second stacks and anouter diameter portion of the coil adjacent the interior surfaces of theouter teeth of the first and the second stacks.
 14. The primary of claim13, further comprising a housing having an encoder locator with anencoder read head for the linear drive motor mounted therein and stackassembly locator with the stack assembly mounted therein, the encoderlocator and the stack assembly locator all being synchronized with asecondary of the linear drive motor.
 15. The primary of claim 14,further comprising fluid passages formed in the housing communicatingwith the stacks.
 16. The primary of claim 14, wherein the inner toothhas a length along a direction transverse to the inner tooth width, andthe outer tooth has a length extending from a direction transverse tothe outer tooth width, and the inner tooth length is less than the outertooth and length.
 17. The primary of claim 14, wherein the outer toothof the first and second stacks each has a projection extending in adirection that is traverse to the width dimensions of the outer tooth.18. The primary of claim 14, wherein the stacks comprise an annealed lowcarbon steel.
 19. The primary of claim 14, wherein the stacks are formedfrom a magnetic stainless steel.
 20. The primary of claim 14, whereinbottom surfaces of the teeth are arcuate and conform to a curvedsecondary of the linear drive motor.
 21. The primary of claim 14,further comprising epoxy coating the stack assembly.
 22. The primary ofclaim 14, wherein the housing has at least one additional stack assemblylocator with at least one additional like stack assembly mountedtherein, the at least one additional stack assembly locator beingshifted relative to the stack assembly mounted therein for creating skewin the alignment of the teeth of the primary relative to teeth of asecondary.
 23. The primary of claim 14, wherein the inner teeth of thefirst and second stacks each have a ledge extending from theirrespective exterior surfaces with the magnet abutting the ledge.
 24. Theprimary of claim 23, wherein the ledge has a dimension corresponding toan amount of skew in the alignment of the teeth of the primary relativeto teeth of a secondary.
 25. The primary of claim 14, wherein thehousing has a first passageway configured to deliver cooling fluidadjacent the stack assembly locator.
 26. The primary of claim 25,wherein the first passageway communicates with at least one of thestacks in the stack assembly.
 27. The primary of claim 26, furthercomprising ports in the stack assembly that form a fluid tightconnection with the first passageway in the housing when the stackassembly is mounted in the stack assembly locator of the housing. 28.The primary of claim 27, wherein the housing has a second passagewayconfigured to receive fluid from the stack assembly.